On 17 Nov, 16:32, Tom Anderson wrote:
Could it introduce performance pollution issues, though, where troubles on
the Northern City lead to problems in the Thameslink core? With Finsbury
Park becoming a sort of overground Camden Town! I think the only way to
absolutely rule that out would be, as with Camden Town, to split the
current two-branch route (possibly requiring reinstating some platforms at
FP?), and have, say, all Hertford trains running to the Thameslink core,
and all Hertford loop trains to Moorgate (or vice versa).

Your starting point would be making all six tracks between Finsbury
Park and Alexandra Palace usable by passenger trains, and if we want
segrgation, due to the junction layout at AP the outermost tracks
would be to/from Hertford and the middle four to/from Welwyn. I think
there's actually enough flexibility at FP to provide segregated routes
to/from Moorgate and KX/Thameslink either way round, assuming you're
willing to rebuild the disused islands.

However, I think you'd end up with a lopsided service if you did this.
I don't think either inner branch needs the 15 tph Moorgate could
handle, but equally I don't think either would be happy with 4 tph
(or at best 8) to Thameslink. Thus you'd probably want the branched
segregated off-peak, with extra trains to Moorgate from the normally-
TL branch in the peaks.

U